1. Technical Field
This disclosure relates to a system and method for improving a tool tip path of a multi-axis machine by testing and compensating for tool misalignment, and in some embodiments, is directed to a system and method for improving a tool tip path of a waterjet cutting machine by testing and compensating for tool misalignment.
2. Description of the Related Art
High-pressure fluid jets, including high-pressure abrasive waterjets, are used to cut a wide variety of materials in many different industries. Abrasive waterjets have proven to be especially useful in cutting difficult, thick, or aggregate materials, such as thick metal, glass, or ceramic materials. Systems for generating high-pressure abrasive waterjets are currently available, such as, for example, the Mach 4™ 5-axis abrasive waterjet system manufactured by Flow International Corporation, the assignee of the present invention, as well as other systems that include an abrasive waterjet cutting head assembly mounted to an articulated robotic arm. Other examples of abrasive waterjet cutting systems are shown and described in Flow's U.S. Pat. No. 5,643,058, which is incorporated herein by reference. The terms “high-pressure fluid jet” and “jet” should be understood to incorporate all types of high-pressure fluid jets, including but not limited to, high-pressure waterjets and high-pressure abrasive waterjets. In such systems, high-pressure fluid, typically water, flows through an orifice in a cutting head to form a high-pressure jet, into which abrasive particles are combined as the jet flows through a mixing tube. The high-pressure abrasive waterjet is discharged from the mixing tube and directed toward a workpiece to cut the workpiece along a designated path.
Various systems are currently available to move a high-pressure fluid jet along a designated path. Such systems may commonly be referred to, for example, as three-axis and five-axis machines. Conventional three-axis machines mount the cutting head assembly in such a way that it can move along an x-y plane and perpendicular along a z-axis, namely toward and away from the workpiece. In this manner, the high-pressure fluid jet generated by the cutting head assembly is moved along the designated path in an x-y plane, and is raised and lowered relative to the workpiece, as may be desired. Conventional five-axis machines work in a similar manner but provide for movement about two additional non-parallel rotary axes. Other systems may include a cutting head assembly mounted to an articulated robotic arm, such as, for example, a 6-axis robotic arm which articulates about six separate rotary axes.
Computer-aided manufacturing (CAM) processes may be used to efficiently drive or control such conventional machines along a designated path, such as by enabling two-dimensional or three-dimensional models of workpieces generated using computer-aided design (i.e., CAD models) to be used to generate code to drive the machines. For example, a CAD model may be used to generate instructions to drive the appropriate controls and motors of the machine to manipulate the machine about its translational and/or rotary axes to cut or process a workpiece as reflected in the model.
Manipulating a waterjet about five or six axes may be particularly useful for a variety of reasons, for example, to cut a three-dimensional shape. To facilitate accurate machining of complex parts using a 5-axis or 6-axis machine it may be advantageous to know the precise spatial relationship between a tool of the machine and an expected tool location defined by the design of the machine, and make adjustments for the same. The expected tool location may be dependent on a number of factors, including machine configuration. For example, in a 5-axis waterjet cutting machine having three translational axes and two non-parallel rotary axes that converge to form a machine focal point, the expected tool location may be located in line with or a selected offset distance from the machine focal point. In other machines, an expected tool location may be positioned relative to a tool reference frame of a terminal component or link of the machine.
In some instances, it is beneficial to align a tool of a machine with the machine's focal point. To set up or test whether a tool of the machine is aligned with the focal point or within a generally accepted tolerance range, it is known to perform manual measurements and physically adjust the alignment of the system based on such measurements, for example, as described below.
A portion of a manual focal point testing and tool alignment apparatus and process is illustrated in FIG. 1, which shows a 5-axis abrasive waterjet machine loaded with a spherical probe at the working end of the machine. A dial indicator is used adjacent the spherical probe to measure the change in position of the surface of the probe as the machine is instructed to move through various orientations, such as, for example, as a wrist of the machine is rotated about a primary rotary axis. Based on the measurements obtained, a technician then physically adjusts the location of the probe by loosening appropriate bolts, adjusting the assembly holding the probe and retightening the bolts to compensate for the perceived misalignment. This process is repeated with the dial gage posed in different locations and orientations to capture adjustments that may be needed due to misalignment between the probe and the machine focal point. This process requires iterative measurements and adjustments as the physical adjustment of the probe with respect to one axis of rotation or translation can cause misalignment with respect to the other axes of rotation or translation. The manual testing and alignment process generally requires a skilled technician. The process is also prone to errors and can be extremely laborious and time-consuming resulting in extended periods of machine downtime. Still further, because the process requires the replacement of a probe with a cutting head or other tool it is prone to the introduction of misalignment at the time the probe is exchanged with the cutting head or other tool prior to processing a workpiece.